Caption: Documenting fossils, Sima de los Huesos. Archaeologists documenting and mapping fossils found at Sima de los Huesos (Pit of Bones). The fossils are being mapped on a scale of 1:1. Sima de los Huesos is one of several sites in Sierra de Atapuerca, Spain, that have been studied on and off over the past century, leading to a massive advancement in the understanding of human evolution. In 2000, Sierra de Atapuerca was made a world heritage site by UNESCO.